Lever-arm vibration damper for a rotor of a gas turbine engine

ABSTRACT

A vibration damper for a rotor blade of a gas turbine engine, includes a plate for placing between an inner bearing surface and an outer bearing surface of the rotor, the bearing surfaces extending in directions that are substantially axial and being radially spaced apart from each other, the plate being folded so as to form two plate portions that are inclined relative to each other, the mass of the plate being distributed in such a manner that its center of gravity is situated on the side of one of these plate portions, the free end of the other plate portion being designed to bear radially against the inner bearing surface, and the junction zone between the two plate portions being designed to bear radially against the outer bearing surface under the effect of centrifugal force when the rotor is rotating so as to provide axial sealing against gas.

BACKGROUND OF THE INVENTION

The present invention relates to the general field of damping the vibration that appears in operation between the outer platforms of two adjacent rotor blades in a gas turbine engine.

A rotor of a gas turbine engine, such as a rotary wheel of a low pressure turbine stage in a turbojet, for example, comprises a disk having a plurality of blades mounted thereon. At its free radial end, each blade presents a transverse element referred to as an “outer platform” that serves in particular to define the outside of the flow passage for the gas stream passing through the turbine.

The outer platform of such a blade has an upstream edge and a downstream edge, which edges extend perpendicularly to the flow direction of the gas stream. These edges are connected together via two lateral edges whereby the outer platform of a blade comes into contact with the outer platforms of two blades of the rotor wheel that are directly adjacent thereto.

Generally, with metal blades, these lateral edges, present a so-called “Z” profile, i.e. each of them has two axial portions that are connected together by a substantially transverse portion. In order to damp the vibration to which the blades are subjected while the turbine is in operation, it is known to mount the blades on the disk with pre-stress in twisting about their respective main axes. At the outer platform of any particular blade, this twist gives rise to the transverse portions of the outer platform of the blade being pressed against the transverse portions of the outer platforms of the adjacent blades. The contact and friction forces that are generated in this way between the outer platforms of the blades serve to dissipate the vibratory energy that results from operation of the turbine.

Nevertheless, such vibration damping is not applicable to rotors having blades that are made of composite material. Specifically, when using ceramic matrix composite (CMC) material blades, twisting the blades generates stresses that are too high compared with the strength of the composite material. Furthermore, using blades made of composite material also has the drawback of giving rise to large steps or large amounts of clearance between the outer platforms of adjacent blades in the event of the blades tilting relative to one another.

OBJECT AND SUMMARY OF THE INVENTION

A main object of the present invention is thus to mitigate such drawbacks by proposing effective damping of the vibration between the outer platforms of adjacent blades made of composite material and without generating excessive stress in the blades.

This object is achieved by a vibration damper for a rotor blade of a gas turbine engine, the damper comprising a plate for placing between an inner bearing surface and an outer bearing surface of the rotor, the bearing surfaces extending in directions that are substantially axial and being radially spaced apart from each other, the plate being folded so as to form two plate portions that are inclined relative to each other, the mass of the plate being distributed in such a manner that its center of gravity is situated on the side of one of these plate portions, the free end of the other plate portion being designed to bear radially against the inner bearing surface, and the junction zone between the two plate portions being designed to bear radially against the outer bearing surface under the effect of centrifugal force when the rotor is rotating, thereby providing axial sealing against gas.

In operation, under the effect of centrifugal force when the rotor is rotating, the junction zone between the two portions of the damper plate comes to bear against the under side of the outer bearing surface of the rotor. Given the particular distribution of mass in the plate, this centrifugal force then creates a lever arm between the center of gravity of the plate and its free end that is bearing radially against the inner bearing surface. In operation, this lever arm thus ensures permanent contact of the plate against both the inner and the outer bearing surfaces, in particular in the event of large steps or large amounts of clearance between the outer platforms of the blades, thereby providing axial sealing against gas. Furthermore, in operation, the junction zone between the two plate portions rubs against the outer bearing surface of the rotor. This friction serves to dissipate the vibratory energy associated with rotation of the rotor. No stress is applied to the blades in order to obtain such energy dissipation. This serves to increase the lifetime of the blades.

Advantageously, the damper further includes means for holding the plate between the two bearing surfaces of the rotor when the rotor is stopped. For this purpose, the plate may include at least one holder tab that extends in a direction that is substantially inclined relative to the radial direction and that is designed to pass through the outer bearing surface.

The invention also provides a rotor element of a gas turbine engine, the element comprising first and second mutually adjacent blades, the first blade having, at a radially free end, a portion constituting a spoiler outer platform without a portion constituting a wiper outer platform, and the second blade having, at a radially free end, a portion constituting a wiper outer platform without a portion constituting a spoiler outer platform, and a vibration damper as defined above, with the plate thereof being arranged between the spoiler outer platform of the first blade forming an inner bearing surface and the wiper outer platform of the second blade forming an outer bearing surface.

The invention also provides a rotor element of a gas turbine engine, the element comprising a pair of mutually adjacent blades, each comprising an airfoil presenting two faces, each connecting a leading edge to a trailing edge of the blade, each blade having a single portion extending from each of the faces of its airfoil, one of these portions forming a spoiler outer platform and the other portion forming a wiper outer platform, and a vibration damper as defined above, with the plate thereof being arranged between the spoiler outer platform of one of the blades forming an inner bearing surface and the wiper outer platform of the other blade forming an outer bearing surface.

The mass of the damper plate may lie in the range 1% to 10%—and preferably lies in the range 4% to 6%—of the mass of a blade.

The damper plate may be positioned between the bearing surfaces in such a manner that the portion having its free end bearing radially against the inner bearing surface is located on the upstream side. As a result, the plate, and more particularly its portion provided with the free end bearing against the inner bearing surface, serves to provide sealing against the gas passing through the gas turbine.

The invention also provides a rotor element of a gas turbine engine, the element comprising a blade having an airfoil, a root for mounting in a disk of the rotor, and an inner platform situated between the root and the airfoil, and a vibration damper as defined above, with the plate thereof designed to be arranged between an outside surface of the disk forming an inner bearing surface and an inside surface of the platform of the blade forming an outer bearing surface.

The invention also provides a gas turbine engine rotor having a plurality of rotor elements as defined above. Finally, the invention also provides a gas turbine engine including at least one such rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention appear from the following description made with reference to the accompanying drawings that show embodiments having no limiting character. In the figures:

FIGS. 1 and 2 are diagrams showing how a vibration damper of the invention is mounted between the outer platforms of two composite material blades having shapes that are complementary, of the “even-odd” type;

FIGS. 3 and 4 are views of the outer platforms of the two blades of FIG. 2, respectively from upstream and from above;

FIGS. 5A to 5C show how the damper moves in the event of radial clearance between the outer platforms of the blades;

FIGS. 6 to 8 are diagrams showing how a vibration damper of the invention is implanted between the outer platforms of two composite material blades having complementary shapes of the “asymmetrical” type; and

FIGS. 9 and 10 are diagrams showing how a vibration damper is implanted in another embodiment of the invention between the inner platforms of two adjacent blades.

DETAILED DESCRIPTION OF EMBODIMENTS

The invention is applicable to various types of gas turbine engine blade, in particular to compressor blades and to turbine blades of various gas turbine spools, for example to rotor blades of a low pressure turbine stage in an aviation turbomachine, such as those shown in FIGS. 1 to 4.

In well-known manner, the rotor 10 of a low pressure turbine stage of a turbomachine comprises a disk 12 (shown in part) having an axis of rotation X-X and with a plurality of blades mounted thereon. For reasons of simplification, only two blades are shown in FIGS. 1 and 2.

The blades may be made of metal or they may be made of composite material, and in particular of ceramic matrix composite (CMC) material. The invention applies more particularly (but not exclusively) to composite material blades of the kind said to be of complementary shapes, of the “even-odd” blade type or of the “asymmetrical” blade type.

In the embodiment of FIGS. 1 and 2, the blades 100 and 200 are of the “even-odd” type. French patent application FR 10/55160 filed in the joint names of Snecma Propulsion Solide and Snecma describes the shape of such even-odd blades and the method of making them.

The first blade 100 comprises an airfoil 102, a root 104, e.g. having a section in the shape of a bulb extended by a tang 106, an inner platform 108 situated between the tang and the airfoil, and a spoiler outer platform 110 situated in the vicinity of the free end of the airfoil.

The airfoil 102 extends longitudinally between the inner platform 108 and the outer platform 110 and presents a curved profile in cross-section between its leading edge 102 a and its trailing edge 102 b. The first blade 100 is mounted on the rotor disk 12 by engaging its root 104 in a housing 14 of complementary shape formed in the periphery of the disk.

At its radially outer end, the airfoil 102 is connected to the outer platform 110 which defines the outside of the flow passage for the gas stream passing through the turbine. In its upstream and downstream end portions (upstream and downstream relative to the flow direction of the gas stream), the outer platform 110 terminates with overlap spoilers 112. Furthermore, it should be observed that the first blade does not have wipers on its outer platform at its radially outer end.

The second blade 200 is designed to co-operate with the above-described first blade 100 so as to form an even-odd type pair of blades.

The second blade 200 comprises an airfoil 202, a root 204 extended by a tang 206, an inner platform 208 situated between the tang and the airfoil, and an outer platform 210 having wipers situated in the vicinity of the free end of the airfoil. The airfoil 202 extends longitudinally between the inner platform 208 and the outer platform 210 with wipers and presents in cross-section a curved profile between its leading edge 202 a and its trailing edge 202 b. The second blade 200 is mounted on the rotor disk 12 by engaging its root 204 in a housing 14 of complementary shape formed in the periphery of the disk. Furthermore, it should be observed that this second blade does not have an outer platform with spoilers at its radially outer end.

As shown in FIG. 2, when the first and second blades 100 and 200 are mounted beside each other on the rotor disk 12, a portion of the wiper outer platform 210 of the second blade 200 takes up a position “above” a portion of the spoiler outer platform with spoilers 110 of the first blade 100.

Furthermore, as shown in FIG. 5A, the inside surface 210 a of this portion of the wiper outer platform faces the outside surface 110 a of said portion of the spoiler outer platform. It should be observed that this inside surface 210 a and outside surface 110 a extend in directions that are substantially axial and that are radially spaced apart from each other by a gap e.

In operation, the blades 100, 200 of the rotor are subjected to vibration that needs to be damped. For this purpose, provision is made to house vibration dampers 300 between the outer platforms of a pair of blades 100, 200 as described above (see FIGS. 3 and 4).

The vibration damper 300 of the invention comprises a plate, e.g. made of metal and of substantially rectangular general shape, which plate is positioned between the outside surface 110 a of the spoiler outer platform 110 of the first blade (forming the inner bearing surface of the rotor in the meaning of the invention) and the inside surface 210 a of the wiper outer platform 210 of the second blade (forming the outer bearing surface of the rotor in the meaning of the invention).

This plate is folded so as to form two plate portions that are inclined relative to each other, namely a first portion 304 a and a second portion 304 b. More precisely, the first portion 304 a of the plate is arranged on the upstream side (upstream relative to the flow direction of the gas stream) and the second portion 304 b is positioned on the downstream side.

The junction zone between the two plate portions 304 a and 304 b may be constituted by a fold line 302, as shown in FIGS. 1, 5A to 5C, and 6. Nevertheless, this junction zone could alternatively be constituted by one or more points.

Furthermore, as shown in FIG. 5A, the free end 306 of the first portion 304 a of the plate comes to bear radially against the outside surface 110 a of the spoiler outer platform 110 of the first blade.

Another feature of the vibration damper of the invention is that the mass of the plate is distributed in such a manner that its center of gravity (represented by point G in FIG. 5A) is situated on the side of the second portion 304 b of the plate.

As a result, under the effect of centrifugal force when the disk is rotating, the fold line 302 of the plate comes to press under the inside surface 210 a of the wiper outer platform 210 of the second blade. Given the particular distribution of the mass of the plate, this centrifugal force creates a lever arm between the center of gravity G of the plate and the free end 306 of the first portion 304 a of the plate, which is bearing radially against the outside surface 110 a of the spoiler outer platform of the first blade. In operation, this lever arm thus ensures permanent contact of the plate against the inner and outer bearing surfaces.

Such permanent contact of the plate against the inner and outer bearing surfaces serves firstly to dissipate by friction the vibratory energy associated with the disk rotating, and secondly to provide sealing relative to the gas flowing through the turbine (by preventing the gas from penetrating from upstream between the outer platforms of the blades).

Furthermore, as shown in FIGS. 5B and 5C, the particular shape of the vibration damper of the invention adapts well to radial clearances appearing between the outer platforms of adjacent blades (as can happen as a result of the blades tilting relative to one another).

In these figures, the respective outer platforms 110, 210 of the two blades are shown spaced apart from each other by gaps e1 and e2 that are greater than the gap e of FIG. 5A, the gap e2 being the greatest that the damper can accommodate. In these figures, it can be seen that regardless of the gap between the outer platforms 110 and 210, the free end 306 of the first portion 304 a of the plate and the fold line 302 of the plate always remain in contact with their respective bearing surfaces. As a result, the damper functions of dissipating vibratory energy and of providing sealing continue to be performed even in the event of a large amount of radial clearance between the outer platforms.

The vibration damper possesses mass that lies in the range 1% to 10%—and preferably in the range 4% to 6%—of the mass of the blades 100 and 200 between which it is mounted. Such a mass enables the plate to perform its vibration damper function well.

The vibration damper of FIGS. 1 to 4 also has means for holding the plate 300 between the wiper outer platform 210 of the second blade and the spoiler outer platform 110 of the first blade.

To this end, the plate 300 has at least one—and preferably two—holder tabs 308 that extend in a direction that is substantially inclined relative to the radial direction and that serve to pass through orifices 212 pierced through the wiper outer platform 210 of the second blade. More precisely, these holder tabs 308 are secured to the second portion 304 b of the plate. As a result, when the rotor disk stops, these holder tabs serve to prevent the vibration damper escaping from its position between the outer platforms of the blades.

FIGS. 6 to 8 are diagrams showing how an above-described vibration damper 300 is installed relative to blades presenting complementary shapes of the “asymmetrical” blade type.

Patent application FR 10/55161 filed jointly in the names of Snecma Propulsion Solide and Snecma describes the shape of such assymmetrical blades and the method of making them.

The blades 400 of the low pressure turbine stage are all substantially identical to one another. Each blade has an airfoil 402, a root (not shown) extended by a tang (not shown), an inner platform (not shown) situated between the tang and the airfoil, a portion forming a spoiler outer platform 414, and a portion forming a wiper outer platform 416.

The airfoil 402 extends longitudinally between its root and its tip and in cross-section it presents a curved profile of varying thickness that defines two faces 418 and 420, corresponding respectively to the suction side face and to the pressure side face of the airfoil, each connecting the leading edge 402 a to the trailing edge 402 b of the airfoil. The blade 400 is mounted on a turbine rotor (not shown) by engaging its root in a housing of complementary shape formed at the periphery of the rotor.

The blade 402 is also connected at its radially outer end and via its suction side face 418 to the portion forming the spoiler outer platform 414 that defines the outside of the flow passage for the gas stream passing through the turbine. On this suction face 418, the airfoil does not have a wiper outer platform portion. Similarly, on its pressure side face 420, the airfoil 402 is connected at its radially outer end to the portion forming the wiper outer platform 416 and it does not have a portion forming a spoiler outer platform. In other words, each blade has a single portion extending from each of the faces 418 and 420 of its airfoil 402.

As shown in FIGS. 7 and 8, when they are mounted side by side on a rotor disk, the blades 400 co-operate with one another in such a manner that the portion forming a wiper outer platform 416 takes up a position “above” the portion forming the spoiler outer platform 414 of the adjacent blade, defining a radial gap between these portions.

A vibration damper 300 of the invention may be housed in this gap (the damper being strictly identical to that described with reference to FIGS. 1 to 4, and 5A to 5C).

The plate of each vibration damper is arranged more precisely between the outside surface 414 a of the portion forming the spoiler outer platform 414 of one blade (constituting an inner bearing surface of the rotor in the meaning of the invention) and the inside surface 416 a of the portion forming the wiper outer platform 416 of the adjacent blade (constituting an outer bearing surface of the rotor in the meaning of the invention).

In this position, the free end 306 of the first plate portion comes to bear radially against the outside surface 414 a of the portion forming the spoiler outer platform 414 of one blade and under the effect of centrifugal force when the rotor is rotating, the fold line 302 of the plate comes to bear radially against the inside surface 416 a of the portion forming the wiper outer platform 416 of the adjacent blade.

This vibration damper dissipates vibratory energy and provides sealing in the same manner as that described for the above embodiment, and that is not described again.

It should be observed that the vibration damper 300 has two holder tabs 308 that pass through orifices 418 pierced in the wiper portion of the outer platform 416 of the corresponding blade in order to hold the plate between the two bearing surfaces when the rotor disk is stopped.

With reference to FIGS. 9 and 10, there follows a description of a vibration damper 300′ in another embodiment of the invention that is designed to be received at the level of the inner platforms of the rotor blades, these blades possibly being blades of complementary shapes (of the even-odd or asymmetrical type) as described above or blades of the kind commonly used in the field of gas turbine engines.

FIGS. 9 and 10 show part of a rotor disk 12 and two blades 500 mounted adjacent to each other on the disk by having their roots 504 engaged in housings 14 of complementary shape arranged in the periphery of the disk. Each blade 500 includes in particular an airfoil 502, a root 504 extended by a tang 506, and an inner platform 508 situated between the tang and the airfoil.

The vibration damper 300′ comprises a plate, e.g. made of metal and of substantially rectangular general shape, which plate is disposed between the outside surface 12 a of the rotor disk 12 (forming an inner bearing surface of the rotor in the meaning of the invention) and the inside surface 508 a of the inner platforms 508 of the two blades (forming an outer bearing surface of the rotor in the meaning of the invention). Circumferentially, the damper plates extends between the two blade platforms 508.

As in the preceding embodiment, the plate is folded in a junction zone formed by a fold line 302′ so as to form two plate portions that are inclined relative to each other, namely a first portion 304′a and a second portion 304′b. The free end 306′ of the first portion 304′a of the plate (arranged on the upstream side) comes to bear radially against the outside surface 12 a of the rotor disk 12. Furthermore, the mass of the plate is distributed in such a manner that its center of gravity (represented by the point G in FIG. 9) is situated on the side of the second portion 304′b of the plate.

As a result, under the effect of centrifugal force when the disk is rotating, the fold line 302′ of the plate comes to bear against the inside surface 508 a of the inner platforms 508 of the two blades. Given the particular distribution of mass in the plate, this centrifugal force creates a lever arm between the center of gravity G of the plate and the free end 306′ of the first portion 304′a of the plate that is bearing radially, thereby ensuring permanent contact in operation of the plate against the inner and outer bearing surfaces.

Such permanent contact of the plate against the inner and outer bearing surfaces serves firstly to ensure that the vibratory energy associated with the rotation of the disk is dissipated by friction, and secondly provides sealing relative to the gas flowing through the turbine (preventing the gas from penetrating from the flow passage between the platforms of the blades).

Compared with the other embodiments described with reference to FIGS. 1 to 4, the vibration damper 300′ does not have any holder tabs. 

1. A vibration damper for a rotor blade of a gas turbine engine, the damper comprising a plate for placing between an inner bearing surface and an outer bearing surface of the rotor, the bearing surfaces extending in directions that are substantially axial and being radially spaced apart from each other, the plate being folded so as to form two plate portions that are inclined relative to each other, the mass of the plate being distributed in such a manner that its center of gravity is situated on the side of one of these plate portions, the free end of the other plate portion being designed to bear radially against the inner bearing surface, and the junction zone between the two plate portions being designed to bear radially against the outer bearing surface under the effect of centrifugal force when the rotor is rotating, thereby providing axial sealing against gas.
 2. A damper according to claim 1, further including a holder configured to hold the plate between the two bearing surfaces of the rotor when the rotor is stopped.
 3. A damper according to claim 2, wherein the plate includes at least one holder tab that extends in a direction that is substantially inclined relative to the radial direction and that is designed to pass through the outer bearing surface.
 4. A rotor element of a gas turbine engine, the element comprising: first and second mutually adjacent blades, the first blade having, at a radially free end, a portion constituting a spoiler outer platform without a portion constituting a wiper outer platform, and the second blade having, at a radially free end, a portion constituting a wiper outer platform without a portion constituting a spoiler outer platform; and a vibration damper according to claim 1, with the plate thereof being arranged between the spoiler outer platform of the first blade forming an inner bearing surface and the wiper outer platform of the second blade forming an outer bearing surface.
 5. A rotor element of a gas turbine engine, the element comprising: a pair of mutually adjacent blades, each comprising an airfoil presenting two faces, each connecting a leading edge to a trailing edge of the blade, each blade having a single portion extending from each of the faces of its airfoil, one of these portions forming a spoiler outer platform and the other portion forming a wiper outer platform; and a vibration damper according to claim 1, with the plate thereof being arranged between the spoiler outer platform of one of the blades forming an inner bearing surface and the wiper outer platform of the other blade forming an outer bearing surface.
 6. An element according to claim 4, wherein the mass of the damper plate lies in the range 1% to 10% of the mass of a blade.
 7. An element according to claim 4, wherein the mass of the damper plate lies in the range 4% to 6% of the mass of a blade.
 8. An element according to claim 4, wherein the damper plate is positioned between the bearing surfaces in such a manner that the portion having its free end bearing radially against the inner bearing surface is located on the upstream side.
 9. A rotor element of a gas turbine engine, the element comprising: a blade having an airfoil, a root for mounting in a disk of the rotor, and an inner platform situated between the root and the airfoil; and a vibration damper according to claim 1, with the plate thereof designed to be arranged between an outside surface of the disk forming an inner bearing surface and an inside surface of the platform of the blade forming an outer bearing surface.
 10. An element according to claim 4, wherein the blades are made of composite material.
 11. A rotor of a gas turbine engine including a plurality of elements according to claim
 4. 12. A gas turbine engine including at least one rotor according to claim
 11. 